In the manufacturing process of an electronic package, the mounting of a chip (device) on a substrate, usually done through soldering, is called "first level packaging". This stage of the process needs to be performed in a "clean" environment to avoid that unwanted particles deposit on the module obtained, before the module is encapsulated, usually with a resin, and the circuits are protected by external agents. For this reason the whole process is carried on in a so-called "Clean Room", which according to industry standards must be at least of class 100000. This means that in a cubic meter there are no more than 100000 particles with dimension less than 3 .mu.m. As an example, in IBM manufacturing lines the Clean Rooms are of class 30000.
Notwithstanding these precautions it can happen that particles of organic nature (eg. coming from a human body such as skin or hair) or of metallic nature (e.g. from moving mechanical machinery) deposit on the module.
The removal of the particles from the module, before the encapsulation is essential for the functionality of the final package. The presence of particles of any nature between the circuits of the substrate can be very harmful. This is particularly true if the increasing reduction of dimensions in the electronic standards is considered. What, in the past, used to be a "cosmetic" problem, with the reduced space between the circuit lines is becoming a vital requirement. It is likely that smaller and smaller particles will become more and more dangerous.
A technique which is normally used to remove the unwanted particles is to wash the modules with Perchlorethylene (PCE) which provides a grease removal. This technique, however does not give the assurance of a complete removal of the particles. For this reason, a manual check with the aid of microscopes must be performed afterwards and the residual particles manually removed with brushes and scrapers.
It should be immediately evident that the above described technique is very laborious and also not completely reliable, because of the human intervention. Furthermore, the interruption of the mechanical handling of the modules for the manual checking and refinement leaves open the eventuality of contamination during the waiting times and the moving of the modules.
It is an object of the present invention to provide a technique which overcomes the above drawbacks.